Electrically-conductive elements and their manufacture



A ril 19, 1966 Filed Jan. 2, 1962 AND THEIR MANUFACTURE (SJ) O 6 2 4 l 91 59, 1 1" ,3 \1\ij/| LJ/ 4531 l'l E 1' O INVENTOR.

wILLIAM SHULVER WILLIAM H. MILLER L; I9," THOMAS L.ATTER|DGE ALFREDMARzoccI-II FIG. 1

ATTORNEYS 2 Sheets-Sheet 1 p 19, 1966 w. SHULVER ETAL 3,247,020

ELECTRIGALLY-CONDUGTIVE ELEMENTS AND THEIR MANUFACTURE 7 Filed Jan. 2,1962 2 Sheets-Sheet 2 FIG.4.

INVEN TOR. WILLIAM SHULVER WILLIAM H. MILLER THOMAS LALTERIDGE ALFREDMARZOCCHI ATTORNEYS United States Patent 3,247,020ELECTRICALLY-CQNDUCTIVE ELEMENTS AND THEIR MANUFACTURE William Shulver,Saylcsville, William H. Miller, Chepachet, Thomas Le Roy Atteridge,Woonsocket, and Alfred Marzocchi, Cumberland, R.I., assignors toOwens-Corning Fiberglas Corporation, a corporation of Delaware FiledJan. 2, 1%2, Ser. No. 163,388 9 Claims. (Cl. 117-226) This applicationis a continuation-in-part of our former copending application SerialNumber 88,542, filed February 10, 1961.

This invention relates to a method of applying anelectrically-conductive coating to the outer surface of elongated glassfibers and the resultant products, and more particularly to a method forapplying a semi-conducting coating to glass fiber filaments, theconductance of the coating being accurately predetermined in themanufacturing process, the coating being uniform in its character and ofsubstantially constant properties regardless of the conditionsencountered during use.

It has been proposed in the past to provide elongated glass fibershaving semi-conductive electrical properties. Such coated glass fibershave been proposed for use as resistors, suitable for example as gridleaks or in voltage divider networks. It has been suggested that suchfibers may be woven into fabrics and utilized as sheathing forelectrical cables used in high-voltage systems to result in a condenseraction between the central conductor and the sheathing to avoidlocalized electrical discharge. Tape, braided or woven from the fibers,may also be used as shielding .to reduce the emission of radiointerference signals from communication cables and the like. Suchshielding may also include copper wire as a carrier.

However, problems have arisen in the manufacture of suitable coatedglass fibers. One problem has been to provide coated glass fibers havingacceptable flexural strengths. Another problem has been to provide aconductive ribbon in which the fibers are arranged in parallel alignmentas opposed to being woven or braided. Such parallel alignment isadvantageous in some applications, such as in the communication fieldfor helically wound cable tubing. A further desire has been to providecoated glass fibers which can be utilized as the current carrying coreof an electrical line, such as communication and automobile ignitionwire. In addition to adequate flexural strengths, conditions of flexingexperienced by such flexible structures have tended to yield a rapidloss of the particulate, conductive coating due to an unsatisfactorybond between the inflexible coating and flexible fibrous substrate.

Previous attempts to provide acceptable fibrous glass,

semiconductive structures have included the coating of the fibrousstrands with colloidal suspensions of the conductive medium, similartreatments with suspensions containing an adhesive phase and the in situformation of the conductive medium by means of the carbonization orpyrolysis of a carbonizable, but uncarbonized coating.

All of these attempts have resulted in products which provedunsatisfactory for one reason or another. For example, most of theseproducts possessed a coating which flaked or powdered ofi upon theslightest flexing of the substrate. Others were plagued by greatreductions in flexural and tensile strengths due to prolonged exposureto high temperatures or moisture which was inherent in the processesnecessary for their preparation. Another common defect comprisednonuniform electrical characteristics or characteristics which could notbe consistently reproduced.

Additionally, it has been desired to provide a method for manufacture ofsuch coated glass fibers which is efiicient and inexpensive.

These problems are alleviated in the present invention in which it is anobject to provide a method for manufacturing elongated glass fibershaving an electricallyconductive coating thereon.

An additional object is the provision of glass fibers possessing auniform coating of a controlled quantity of an electroconductivematerial which is strongly adhered to the glass fibers to yield astructure having outstanding properties of semi-conductivity, durabilityand strength.

Another object of the invention is to provide a method for the uniformdistribution of electrically-conductive particles on glass filaments.

A further object of the invention is to provide a method formanufacturing coated glass fibers of predetermined electricalconductivity.

Yet another object of the invention is to provide a process forproducing coated glass fibers in which the semi-conductive electricalproperties may be readily varied.

Another object of the invention is to provide a method for baking theelectrically-conductive coating onto the glass fibers by utilizing aheated drum which is more efiicient and occupies less space than theconventional oven.

A further object of the invention is to employ such a heated drum toflatten a bundle of individual glass filaments during baking of theconductive film to result in a conductive ribbon in which the individualfilaments are in planes substantially parallel to one another.

Another object is to provide an electrically-conductive flat tape by theabove-mentioned process in which the individual filaments are parallelrather than woven or braided.

A still further object of the invention is to apply the initialconductive coating to the glass fiber filaments by means of a bathcontaining suspended electrically-conductive particles, and in which theelectrically-conductive particles are continuously recirculated toresult in a uniform coating on the glass fiber filaments.

A further object of the invention is to provide a die for maintaining aneven distribution of electrically-conductive particles on the glassfibers.

Another object of the invention is to provide means for coating glassfilaments with graphite linters and a resin coating to result in aproduct having superior conductive properties.

A still further object of the invention is to provide a method ofcoating the electrically-conductive glass fibers with a plastic orsimilar film-forming material to result in improved abrasion resistance.

Other objects of this invention will appear in the following descriptionand appended claims, reference being had to the accompanying drawingsforming a part of this specification wherein like reference charactersdesignate corresponding parts in the several views.

In the drawings:

FIGURE 1 is a top plan view of an apparatus utilized in one embodimentof the process of the present invention;

FIGURE 2 is a side elevational view in section of the coating bath takensubstantially along the line 2-2 of FIGURE 1 looking in the direction ofthe arrows;

FIGURE 3 is a perspective view of the heated drum and idler rollutilized to dry and bake the coated glass fiber in the FIGURE 1 process;and

FIGURE 4 is a perspective view of apparatus utilized in a secondembodiment of the present invention.

Before explaining the present invention in detail, it is to beunderstood that the invention is not limited in its application to thedetails of construction and arrangement of parts illustrated in theaccompanying drawings, since the invention is capable of Olr'lelembodiments and of being practiced or carried out in various ways. Also,it is to be understood that the phraseology or terminology employedherein is for the purpose of description and not of limitation.

Referring to FIGURE 1, it may be seen that a creel is provided to hold aplurality of rotatable rolls 12 of glass fiber strands. A strand isdefined for the purpose of this invention as a primary bundle ofcontinuous glass fiber filaments combined in a single compact unitwithout twist. Preferably, the filaments are precoated with a starch orsimilar sizing as is conventional in the manufacture of glass filamentsand which normally comprises 0.5 to 15% by weight of the coatingcomposition. The sizing aids in the handling of the filaments and thestarch is apparently caramelized during the present process to form partof the conductive-coating. This thermal conversion of the precoating andthe consequent improvement of the bond between the fibers and theconductive coating will be subsequently discussed in greater detail.

The creel 10 has two vertical stacks 19, 21 having three levels 20, 22,24, each level holding ten rolls 12 to total sixty rolls. The strands 14are directed from the creel through guide openings in guide structure 26and thence to central eyes 28 wherein ten strands are gathered togetherto form rovings 30.

Each roving 30 passes over roller 32 which is rotatably mounted insupport structure 34. The lower portion of the roller 32 dips into watercontained in pan 36 and wets the roving passing thereover. Alcohol inamounts of from 2 to 5% may be added to the water to provide an improvedprewetting mix. Other wetting agents may be added to the mix as desired.

The roving then passes through a pan 38 which contains, in liquidsuspension, small particles of electricallyconducting material. Theparticles adhere to the roving as it passes tberethrough to form a thinelectrically-conducting film on the roving. Each individual filament ofthe roving will be so coated.

As will be noted in FIGURE 2, the pan 38 is supported on a tablestructure 40. The table 40 also supports a reservoir 42. Fluid is pumpedfrom the bottom of reservoir 42 through conduit 44 by pump 46. Conduit48 extends from the pump upwardly to a point above the pan 38. Spouts 50having closure valves 52 direct streams of fluid 54 into the pan andover the rovings. The pan 38 is canted slightly and the fluid 54constantly runs out of the pan through the open front end 56 back intothe reservoir 42. The purpose of continuously pumping from the reservoirinto the pan and then allowing the fluid to flow back into the reservoiris to keep the fiuid in a well-mixed condition to prevent settling ofthe electrically-conducting particles. In this way, a uniform coating onthe roving is assured. The reservoir 42 is constantly replenished froman external source (not shown).

The coated rovings each pass through openings 57 of predetermined sizein dies 58 provided on the table 40. The dies wipe off the excessparticles and fluid to maintain a uniform coating thickness.Additionally, the dies force the individual filaments together toachieve some degree of mechanical bond therebetween.

The coated rovings extend from the dies 58 over idler roller 60 andthence spirally over heated rotating drum 62. As will be understood, theroving slides sidewise in its spiral path over the drum. For thisreason, it is important to adjust the pressure between the drum androving to avoid binding of the roving with the drum surface. As shown inFIGURE 3, the roving takes approximately ten turns around the drum. Thefunction of the heated drum is to dry the roving and brake theelectrically-conducting particles onto the glass fiber. Additionally,the drum flattens the bundles of glass fibers and, during the bakingprocess, bonds the individual fibers together in substantially parallelarrangement to form a flat ribbon.

Cir

As will be appreciate, the drum diameter and temperature and the numberof times the roving passes thereover may be varied. It has been found,however, that with the roving travelling at 35 feet per minute drumtemperatures in the range of from 550650 F. are preferred. However,temperatures up to 700 F. may be employed. Temperatures in this rangeare made possible by virtue of the highly efiicient thermal transferbetween the drum surface and the coated strands which engage thatsurface. The heat treatment is probably also enhanced by the graduallyincreasing thermal gradient which ensues from the presence of an aqueousphase in the coating composition present upon the treated strand. Auniform thermal transfer from the exterior to the interior of the strandis also derived from the intimate engagement of strand and drum and thecontinual change in the portion of the strand which engages the drum. Inaddition, the flexibility of the strand is maintained as it issimultaneously exposed to heat and a working or drafting effect.

The idler roller 60 is also preferably heated to a temperatureapproximating that of the drum 62. If the idler roller is cool or warm,it will pick up a portion of the coating material fro-m the roving. Thisis, of course, undesirable because such a pickup will make the thicknessof the final coating nonuniform.

After the roving leaves the drum 62, it is wound up on take-up rollers64 and subsequently stored.

More than one coating of electrically-conductive particles may beapplied. For example, one conductor material was made having threecoatings of particles. This material was passed through a 32 foot ovenat 600 F. at the rate of twenty-five feet per minute. Its conductivitywas 4000 ohms per square inch.

A number of different electrically-conductive particles may be utilizedto coat the glass fibers. For example, dispersions or colloidalsuspensions of graphite, carbon black, metals and organotnet-alliccompositions which decompose under heat to form a metallicelectrically-conductive coating may be used. The percentage ofelectrically-conductive particles in the fluid mixture is varieddepending on the desired thickness of the applied coating. Graphite is apreferred material because of its excellent electrical properties andbecause of its lubricating properties. When graphite coated filamentsrub against each other, there is less friction and thus less abrasion.Additionally, elongated carbon particles, such as the graphite lintersdescribed hereinafter in conjunction with the second embodiment of theinvention, may be included in the mixture of electrically-conductiveparticles. It has been found that when such elongated particles areused, less electrically-conductive material is necessary in the coatingand the flexibility of the coating is improved. This may result from thegreater interlinkage and dove-tailing between adjacent elongatedelements as compared with the interlinkage of spherical particles.

One suitable commercially available material which has been used withsuccess is sold under the tradename aquadag. This material is aconcentrated colloidal dispersion of pure electric-furnace graphite inwater. It is a paste consistency with a solids content of 22%. Theaverage particle size is 0.5 micron and the maximum particle size is 4microns. The specific gravity is 1.121 and the boiling point is C. Thematerial is completely miscible with water. This material is preferablydiluted with water, for example, three parts water to one part aquadag,to obtain a fluid which can be pumped and which will give the desiredsurface coating thickness.

While various starches, sugars, glucose, sorbitol, glycerol and the likehave been suggested as the preferred types of compositions for thepreeoating, it should be realized that any organic material capable ofconversion to a carbonized or caramelized condition upon exposure totemperatures below 750 F. are suitable for the practice of theinvention. Specifically, such materials must be thermally transformableat temperatures below 750 F. The phrase thermally transformable isemployed to designate the ability of the materials to be partially orcompletely carbonized or caramelized at the prescribed temperatures. Inaddition, it should be noted that numerous other compositions, as forexample synthetic resins such as polyvinyl acetate, may be thermallytransformed or carbonized at the temperatures involved in the inventiveprocesses.

In addition to the electrically-conductive particles, a binder materialmay be added to the suspension to improve the bond of the particles tothe glass fibers. Prefer-ably, the binder material, if used, is acarbonaceous material which will decompose to form carbon when heated.For example, sugar, starch, glucose, sorbitol, glycerol and the like maybe used. When such materials are heated and thermally decomposed tocarbon, they form an electrical bridge between theelectrically-conductive particles to result in a continuous electricalpath. Quaternary ammonium compounds have also been found useful for thispurpose. It is preferable, however, to avoid or minimize the use of abinder material because the resultant electrical properties when abinder is used are not as good as when the binder is not used, due tothe requisite heterogeneity of the coating.

Alternative to the use of a heated drum, the roving may be passedthrough an oven to dry and bake the roving. As will be appreciated, whenan oven is used the roving is not flattened, and higher temperaturesmust be employed in order to derive an equivalent result.

The products derived from the inventive methods exhibit anelectrical-conductivity which has been previously unequalled with suchmaterials, in respect to either degree or uniformity. In addition, theconductive coating is so well adhered to the fibrous substrate that thecoated structure may be subjected to repetitive, prolonged flexingwithout an appreciable loss of the coating or decrease in conductivity.Still further, the coated structure does not exhibit a diminution offlexural or tensile strengths.

While it is found that some degree of improvement, Within the scope ofimprovement made possible by the invention, may be attributed to thedrum. drying technique, it is believed that a major contribution to therealization of the improvements, is derived from the properties of thefibrous substrate employed and the bond which is obtained as the resultof the effects of the inventive processes upon these substrates andtheir precoatings.

The advantages of drum-drying appear to derive from the high efiiciencyof the conductive transfer of heat from the surface of the drum to theglass filaments, which is attended by rapid and thorough heating. Itfurther serves to provide a structure in a tape-like form with theindividual filaments positioned in a relationship ideal for manysemi-conductive applications.

However, it is believed that the unusual and improved properties of theultimate products are primarily attributable to an improved bonding atthe fiber-coating interface, which may experience an additionalincrement of improvement when conductive, as opposed to radiant, heatingis employed.

It is further believed that the ideal interfacial condition is thedirect result of the presence of a carbonizable, pyrolyzable orcaramelizable material upon the surfaces of the fibers prior to theapplication of the conductive coating and the drying or heat treatmentof that coating. This condition is achieved by the conversion of thematerials at the interface to a partially or completely, carbonized orcaramelized state. It has been demonstrated that film-formingdispersions or solutions of a film-forming material such as starch,sugar, glucose, sorbitol, glycerol and the like, are capable of adheringto the surfaces of glass fibers. In contrast, colloidal suspensions ofcarbon, graphite, metals and organometals may be deposited upon glasssurfaces by dispelling or volatilizing the suspension carrier, but suchmaterials are not actually bonded to the glass and are easily displacedby external contact or the flexing of the glass substrate. Thiscondition is only slightly improved if the conductive suspensions aredeposited upon an organic film of starch or the like which is previouslyformed upon the surface of the glass, since there is no pronouncedcompatibility or adhesion between such organic films and the conductivedeposits.

However, in accordance with the invention, it is believed that asituation favorable to both the compatibility and adhesion of these twodissimilar types of materials is achieved. It has been determined thatwhen organic materials capable of undergoing carbonization, pyrolysis orcaramelization at temperatures below the softeningpoint of the glass,are subjected to such temperatures while positioned upon the glasssurface, the transformed residues still exhibit a strong adhesion to theglass surfaces. For example, glass fibers coated with dextrinized starchwere treated in an oven maintained at 400 F. for three hours andsubsequently immersed in boiling water for three hours. It was foundthat only 50% of the starch was removed despite the severity of thistest, and some of that loss is undoubtedly attributable to the thermaltreatment rather than the attack of the boiling water upon the bond ofthe starch residue to the glass surface. In the conduct of the test itwas found that the starch began to caramelize at 400 F. and that theeffect continued to substantial completion during the three hour heattreatment. This test is cited to illustrate the tenacity of theadherence of caramelized starch residues to glass surfaces.

The term caramelize as used herein is intended to connote a conditionshort of complete carbonization or pyrolysis, wherein the thermallycaramelized material may possess some carbonized portions but isgenerally perceptible as a relatively rigid, plastic, and normallytacky, composition.

If one employs temperatures capable of caramelizing the coating upon theglass fibers while that coating is in intimate engagement with a furthercoating comprising a colloidal suspension of conductive particles, it isapparent that the coating will be caramelized and the particles will bedeposited upon the caramelized surface. It is further apparent that thecaramelized material will be strongly adhered to the glass substrate andthe particles will be strongly adhered to the caramelized material dueto the tacky nature of the latter.

Proceeding further, it is also feasible that a favorable interface willresult if the thermal conditions experienced are in excess of thoserequired for more caramelization, and are adequate for complete orpartial carbonization of the material employed to precoat the glassfibers. For example if the heat treatment is adequate to carbonize thesurface of the coating and merely caramelize that portion of the coatingwhich is immediately adjacent to the glass surface, a desirableassociation of glass to caramelized material, caramelized material tocarbonized material and carbonized material to inorganic conductiveparticles is achieved. The factors of compatibility between thecarbonized material and the inorganic particles, and the adhesion of theremaining strata, are highly conductive to a well-integrated structure.Even if the material employed to precoat the fibers is completelycarbonized, a condition favorable to compatibility is attained whereinthe nature of the structure blends from glass to an in situ carbonizedregion and ultimately to an area comprising deposited carbonaceous ormetallic materials which were present and in intimate engagement withthe precoating upon the fibers, during the thermal conversion of theprecoating to a carbonized condition.

While it is practically impossible to guage or determine the actualnature of the conductive coating to glass interface after subjection tothe inventive processes, it is known that starch employed as a size uponglass fibers is' caramelized after prolonged heat treatment attemperatures in the range of 400 F., and that short exposures at 700-750P. will serve to achieve a similar effect while similar exposures at 900F. in an oven, will result in a substantially complete carbonization ofthe starch. While it is difficult to assess the effect of thesuperimposition of an aqueous dispersion of conductive particles uponthe precoated strand and the divergent thermal effects of conductive andradiant heat treatments, it is safe to assume that the temperatureswhich are preferably employed by the inventive processes (550- 700 P.)will operate to caramelize the precoating and possibly to partially orcompletely carbonize the precoating.

While temperatures of 55()700 F. are preferred when the thermaltreatment is achieved by means of a heated drum, higher temperatures maybe employed with oven treatments. For example, temperatures of as highas 1100 F. may be necessary in the latter type of treatment due to thelimited efficiency of thermal transfer. However, temperatures in excessof 11001200 F. should be avoided with a conventional glass compositionsuch as E glass, in order to avoid achieving the softening point of theglass.

It should also be noted that the precoating may be transformed to acaramelized condition and the conductive particles may then be powderedupon the resultant tacky surface. However, such a method is not asconducive to the formation of a conductive coating possessing both thequantity of coating material and the continuity of the coating derivedfrom the in situ deposition of the conductive particles from a colloidalsuspension.

It has been further found that the electrical properties of the coatedglass fibers may be improved if an electric current is passed throughthe fibers as the fibers are heated to carbonize and bake the coatingthereon. The electric current tends to align the graphite and othercarbon particles. Such alignment links up the particles and improves theconductivity of the coating.

It will be appreciated that the resultant product may be varied withinwide limits. For example, the number of strands and the electricalresistance per foot of the product is capable of being varied asdesired. One product produced consisted of 60 strands and had aresistance of 3000 ohms per foot. It has been found that strands having100 or more filaments and roving having four or more strands areparticularly useful.

Another embodiment of a method for applying an electrically-conductivefilm to glass fibers is illustrated in FIGURE 4. A creel 66 is providedhaving a plurality of rolls 68 to dispense strands 70 of glass fibers.The fibers extend through guide openings in guide structure 72 and passto a central collecting eye 74 where they are formed into a roving 76.At a point just short of entering the gathering eye 74, the strands aresprayed with electrically-conductive linters by means of a flocking gun78. The spray is directed towards the center of the converging strands.The linters are loosely held in the roving by entanglement with thestrands.

Subsequent to passing through the eye 74, the roving 76 passes overtable 80 and through applicator 82. Applicator 82 contains a fluidcoating material (supplied from an external source not shown) and acoating is applied to the roving. The resin acts as a binder and also iselectrically-conductive.

Subsequent to the application of the fluid coating, the roving isdirected into an oven 84 wherein the resin is cured thermally to form atough coating. The thus coated roving is wound up on take-up roll 86.

The roving may be directed through a wiping die before or after bakingin the oven depending upon the compatibilities of the materials. The diemay be either of the rotating or stationary type.

The linters are preferably graphite of a size approxi mately A; to 1inch long. However, elongated metallic particles may also be utilized.If metallic particles are used, a reducing agent such as hydrazine,formaldehyde (or hydride) or the like should be added to reduce theresistance between contacting particles. Graphite linters may bemanufactured by graphitizing natural or synthetic fibers.

The fluid coating for the roving may be an organosol, plastisol or latexresin, such as vinyl or butyl acrylate which is partially hydrolyzed orit may be a coating composition such as a lacquer. In order to obtainmaximum conductivity when using an emulsified resin, it is preferablethat the diluents or plasticizers be reduced to a minimum concentration.Additionally, an improved material will result if the conductiveparticles are adsorbed on the surface prior to application of the resinor coating composition.

The resultant conductive glass fibers will have improved conductivityover that provided by other forms of electrically-conductive materialsbecause of the linear structure of the linters. It has been found thatvery small amounts of such linear material results in superiorconductivity.

In use of the coated linter conductor, current passes through the outerlow conductive coating to the core which contains the linters and thencealong the core to an exit point such as ground where it again passesthrough the outer cover.

It is apparent that new and improved conductive glass elements, andmethods for their preparation, are provided by the present invention.

It is also obvious that various changes, alterations and substitutionsmay be made in the present invention without departing from the spiritof the invention as defined by the following claims:

We claim:

1. An electrically conductive element comprising: a glass fiber, oblongparticles of electrically conductive material positioned adjacent thesurface of said glass fiber with the major dimension of said oblongparticles parallel to the surface of said fiber, and a material selectedfrom the group consisting of residues of caramelizable and ofcarbonizable materials, produced in situ while connecting said glass andparticles by thermal decomposition in a controlled oxidizing atmosphereto bond said electrically conductive particles to said glass.

2. An element as described in claim 1 in which said electricallyconductive particles are selected from the group consisting of plateletsof graphite, and platelets of metals.

3. A method for the preparation of electrically conductive glasscomprising:

(a) coating glass with between 0.5 to 15% by weight of a thermallytransformable material selected from the group consisting ofcaramelizable and carbonizable materials,

(b) positioning upon said thermally transformable material while wettedby water electrically conductive particles with their major dimensionsgenerally parallel to the surface of the glass, and

(c) subjecting the so coated glass to a controlled oxidizing atmosphereand a temperature adequate to achieve the in situ thermal transformationof said thermally transformable material without removing said thermallytransformable material to bond said particles to said glass by means ofthe thermally transformed material, said temperature being below thesoftening point of said glass fibers.

4. A method as described in claim 3 in which electrically-conductiveparticles are selected from the group consisting of graphite, and metalplatelets.

5. A method as claimed by claim 3 in which said thermally transformablematerial is between 0.5 to 15% by weight of starch.

6. A method as claimed by claim 3 in which said thermally transformablematerial is between 0.5 to 15% by weight of sugar,

7. A method as claimed by claim 3 in which said thermally transformablematerial is between 0.5 to 15% by weight of glucose.

8. A method as claimed by claim 3 in which said thermally transformablematerial is between 0.5 to 15% by weight of a carbohydrate, and saidthermally transformed material is heated to a temperature between 400 F.and 750 F.

9. A method as claimed by claim 3 in which said thermally transformaiblematerial is decomposed by being held against a surface heated to atemperature between 400 F. and 750 F. and which surface is exposed tothe atmosphere.

References Cited by the Examiner UNITED STATES PATENTS 869,012 10/1907McQuat et al 117226 X 1,745,939 2/1930 Loewe 117-46 1,771,055 7/1930Pender 117126 2,225,009 12/1940 Hyde 11746 2,341,219 2/1944 Jones 117462,375,178 5/1945 Ruben 117126 2,577,936 12/1951 Waggoner 1171262,584,763 2/1952 Waggoner 117-126 10 2,645,701 7/1953 Kerridge et a1.117126 2,749,255 6/1956 Nack et a1 117126 2,758,948 8/1956 Simon et a1.117216 2,910,383 10/1959 Miller et al. 117126 5 2,917,439 12/1959 Liv117126 2,970,934 2/1961 May 117126 2,979,424 4/1961 Whitehurst et al.11746 X 3,002,862 10/ 1961 Smith-Iohannsen 117226 3,013,328 12/1961Beggs 11746 10 3,029,166 4/1962 Hainsworth et al. 117216 3,030,2374/1962 Price 117126 3,081,202 3/ 1963 Kemp 117126 FOREIGN PATENTS 15626,163 8/1961 Canada.

1,212,187 10/1959 France.

OTHER REFERENCES 0 Morgan, Glass Reinforced Plastics, IntersciencePublishers, New York, 1961, third edition, p. 208 relied on,

RICHARD D. NEVINS, Examiner.

1. AN ELECTRICALLY CONDUCTIVE ELEMENT COMPRISING: A GLASS FIBER, OBLONGPARTICLES OF ELECTRICALLY CONDUCTIVE MATERIAL POSITIONED ADJACENT THESURFACE OF SAID GLASS FIBER WITH THE MAJOR DIMENSION OF SAID OBLONGPARTICLES PARALLEL TO TH SURFACE OF SAID FIBER, AND A MATERIAL SELECTEDFROM THE GROUP CONSISTING OF RESIDUES OF CARAMELIZABLE AND OFCARBONIZABLE MATERIALS, PRODUCED IN SITU WHILE CONNECTING SAID GLASS ANDPARTICLES BY THERMAL DECOMPOSI-